Economist Eric Crampton has drawn attention to a paper in the American Journal of Clinical Nutrition which shows an association between children drinking non-dairy milk, as opposed to cow’s milk, and lower heights.
The press release talks about associations but doesn’t say anything about causality. Nevertheless, the author goes on about the lack of regulation of protein content in non-dairy milk.
And hey, maybe that’s what’s going on. Reduced protein intake could be doing it.
But it looks like the paper doesn’t control for other part of kids’ diets. If it’s likely that kids on almond milk diets or soy milk diets are more likely to be on vegan diets overall or to have other weird diet issues that could also affect protein intake, it seems kinda odd not to adjust for other parts of the diet.
And while they exclude kids with growth-affecting disease from the study, they do include asthma. Some folks exclude dairy as part of trying to control asthma, and inhaled corticosteroids can suppress growth among kids (though they catch up later).
So it would be a bit premature to run the cross-price elasticities of milk with respect to non-dairy substitutes, multiply by the effect of supply management on milk prices to get the substitution into non-dairy because of supply management, then work out how much shorter supply management is making some Canadian kids.
The research was supported by the Canadian Institutes of Health Research Institute of Human Development, Child and Youth Health, and the Institute of Nutrition, Metabolism, and Diabetes and St. Michael’s Hospital Foundation.
The researchers aimed to determine whether there is an association between non-cow milk consumption and lower height in childhood and assess whether cow milk consumption mediates the relation between non-cow milk consumption and height.
They give this background to their study:
Cow milk consumption in childhood has been associated with increased height, which is an important measure of children’s growth and development. Many parents are choosing non-cow milk beverages such as soy and almond milk because of perceived health benefits. However, non-cow milk contains less protein and fat than cow milk and may not have the same effect on height.
The authors say this was a cross-sectional study of 5034 healthy Canadian children aged 24–72 months enrolled in the Applied Research Group for Kids cohort. The primary exposure was the volume of non-cow milk consumption (number of 250-mL cups per day).
Multivariable linear regression was used to determine the association between non-cow milk consumption and height. A mediation analysis was conducted to explore whether cow milk consumption mediated the association between non-cow milk consumption and height.
Results: There was a dose-dependent association between higher noncow milk consumption and lower height (P < 0.0001). For each daily cup of noncow milk consumed, children were 0.4 cm (95% CI: 0.2, 0.8 cm) shorter. In the mediation analysis, lower cow milk consumption only partially mediated the association between noncow milk consumption and lower height. The height difference for a child aged 3 y consuming 3 cups noncow milk/d relative to 3 cups cow milk/d was 1.5 cm (95% CI: 0.8, 2.0 cm).
The paper’s conclusion is that non-cow milk consumption was associated with lower childhood height. Future research is needed to understand the causal relations between non-cow milk consumption and height.